The solar cell market has grown rapidly at a rate of 35% or higher since 2003. The price of polysilicon that is the main material of solar cells temporarily declined in the first half of 2009 and has shown an upward tendency since 2010, but it is predominantly expected that the price of polysilicon will be stabilized at low prices in the future. Thus, the development of a technology for producing highly pure inexpensive polysilicon can lead to increases in competitiveness and market share in the global polysilicon market and will have a great ripple effect on the related industries.
Among current commercial technologies for producing silicon for solar cells, the so-called Siemens process that is a vapor-phase process is most frequently used. This vapor-phase process that comprises reacting metallurgical-grade silicon (MG-Si), produced from silica stone, with HCl or H2 to make a gaseous mixture, purifying the gaseous mixture in a distillation column to remove impurities, and depositing high-purity polysilicon from the resulting silicon rod. This vapor-phase process can be applied to both the semiconductor industry and the solar cell industry, because it can produce high-quality polysilicon. However, the vapor-phase process requires large-scale investment (an equipment investment of about one hundred million Won (Korean currency) per ton of production of polysilicon) and high energy consumption (about 120 kWh/kg), and thus when it is applied to the solar cell industry, it can be a highly expensive process.
For this economic reason, technology for a metallurgical refining process, but not the vapor-phase process, has recently been developed. As used herein, the term “metallurgical refining process” refers to a process of refining metallurgical-grade silicon by slag treatment, segregation, rapid solidification, electron beams, plasma, etc. The metallurgical refining process has advantages in that it can produce polysilicon using energy of ⅕ compared to the vapor-phase process and can reduce the occurrence of environmental pollution because it uses no chlorosilane, and the construction and operation of equipment are safe and convenient.